The line just be yourself is one of those lines I think is often mistranslated. Be yourself, what is it to be you.
Well, first off I'm going to start with what makes up a personality. I'm going to start off by saying you do not have a personality. Your probably thinking I'm off my rocker but take a second and here me out.
Our personality is all in our self image. If you see yourself as a rocker boy, thats what you become. If you see yourself as a loser, guess what, you are. If you see yourself as a charismatic, energetic, life loving, chick magnet, then I'm guessing you are.
Your morals, loves, hopes, dreams are all made up by you. You make yourself up how ever you want.
Now that I destroyed your sense of individualism let me go onto some good news. All this means that you can be what ever you want to be. Take out a pen and paper and spend 1 to 3 hours imagining and meditating on who you want to be. Make it as vivid as possible. Now fake it till you make it. I did not become any good at pickup till I myself started to believe I was a pickup artist.
So if you want to become your vision just hold the mask in front of yourself for long enough and eventually it will no longer be a mask.